This Project will study brain injury and recovery of function in humans with temporal lobe epilepsy (TLE). It will assess cognitive organization, including language and memory, consequent to the initial injury causing the epilepsy. The project will then evaluate cognitive reorganization following anterior temporal lobectomy (ATL) to determine which areas of the brain participate in recovery, and examine pre-operative organization and reorganization after ATL in light of age at the time of first brain injury. Cognitive organization will be assessed in 100 patients with strictly defined unilateral temporal lobe epilepsy before and after ATL. This will be accomplished using specific cognitive tasks (including verbal memory, visual memory, naming) that focally increase cerebral blood flow (CBF). CBF will be measured in the resting state and during task performance with positron emission tomography, using 15-O labelled water. Patient data will be compared with data from healthy controls. Cognitive abilities will be measured by neuropsychometric testing. It is hypothesized that early brain damage (< age 5) in TLE patients causes aberrant localization of temporal lobe functions to other lobes of the brain, particularly contralaterally, compared with normal individuals. this will be manifested as abnormal CBF patterns during task performance. After ATL of a functioning temporal lobe (shown by CBF activation), cognitive impairment will occur, while no impairment will result from ATL of a non-functioning temporal lobe. Recovery from ATL results in new regions in both hemispheres participating in cognitive tasks, demonstrated by different patterns of CBF activation. This is clinically relevant because it is postulated that CBF patterns during task performance will predict: 1) whether or not ATL will adversely affect cognition (particularly memory), and 2) likelihood of seizure relief after ATL.